This invention relates to stable reference voltage sources. More particularly, it is concerned with band gap voltage regulators.
There are many situations which require temperature stable reference voltage sources. For use in integrated circuit form it is necessary that the components of a reference voltage source be compatible with the particular integrated circuit technology. One known type of reference voltage source which is compatible with conventional monolithic integrated circuits is a band gap voltage regulator. Certain parameters of a band gap voltage regulator have negative temperature coefficients and certain have positive temperature coefficients thereby, theoretically, providing an output voltage which is stable despite temperature variations. The stable output voltage obtained from a circuit of this type is approximately equal to the band gap voltage of the semiconductor material employed, typically silicon.
One form of band gap voltage regulator includes two series arrangements of transistors, current sources, and resistances. The two series arrangements are connected in parallel and there is a fixed ratio of relative current flow in the two arrangements. The amount of current flowing in each of the two series arrangements is adjusted to maintain the voltage at a certain point in one arrangement equal to that at a certain point in the other arrangement. The two points are connected to the inputs of an amplifier the output of which controls the current sources, thus providing a self-balancing bridge which adjusts current flow to maintain the two points at the same voltage. The offset voltage of the amplifier, however, may cause a significant differential voltage to be produced between the two points. Although various circuit arrangements have been devised to correct for the error caused by amplifier offset voltage, the residual error may have a significant effect on the stability of the output voltage produced by the regulator.